Calculate the mass fraction and the weight percent of the...

Calculate the mass fraction and the weight percent of the solute in each of these solutions: (a) $20.7 \mathrm{~g} \mathrm{NaCl}$ in $175 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}$. (b) $1.45 \mathrm{~g}$ ethanol in $10.0 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}$. (c) $20.0 \mathrm{~g} \mathrm{CS}_{2}$ in $45.0 \mathrm{~g} \mathrm{CHCl}_{3} .$ (d) $4.00 \mathrm{~mL}$ benzene $(d=0.877 \mathrm{~g} / \mathrm{mL})$ in $120 . \mathrm{g}$ diethyl ether.

Calculate the mass fraction and the weight percent of the solute in each of these solutions:
(a) $20.7 \mathrm{~g} \mathrm{NaCl}$ in $175 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}$.
(b) $1.45 \mathrm{~g}$ ethanol in $10.0 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}$.
(c) $20.0 \mathrm{~g} \mathrm{CS}_{2}$ in $45.0 \mathrm{~g} \mathrm{CHCl}_{3} .$
(d) $4.00 \mathrm{~mL}$ benzene $(d=0.877 \mathrm{~g} / \mathrm{mL})$ in $120 . \mathrm{g}$ diethyl ether.

Key Concepts

Mass Fraction

Mass fraction is defined as the ratio of the mass of the solute to the total mass of the solution. It is a dimensionless quantity that provides a direct measure of the proportion of solute present in a mixture. This concept is fundamental in chemistry when describing the composition of solutions without reference to any specific solvent or solute mass units beyond their ratio.

Weight Percent

Weight percent is a way to express the concentration of a solution, calculated by multiplying the mass fraction of the solute by 100%. It denotes how many grams of solute are present per 100 grams of the solution, offering a percentage representation that is often used in laboratory and industrial settings for ease of communication.

Solute and Solvent

Understanding solute and solvent is crucial when discussing solution concentrations. The solute is the substance that is dissolved, and the solvent is the medium in which the solute is dissolved. Distinguishing between the two is important because the concentration measures and calculations focus on the solute's contribution relative to the overall solution.

Density and Volume Conversion

In some instances, converting between volume and mass is required, especially when a solution component is given in volume and its density is provided. By using the relation mass = density × volume, you can accurately convert a volume measurement to a mass value, ensuring that all components of the solution have consistent units for proper calculation of concentrations.

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